Induction heating apparatus



p N H. A. STRECKLANQJR 2,4025% INDUCTION HEATING APPARATUS Filed May 22,1945 I INVENTOR 29 Harold fl.$irz'c'iiland,.fn

A TTORNE Y Patented June'l8, 1946 Hamid A. Strickland, In, Detroit, Michassignor, by none assignments, to Budd Wheel Company, a corporation ofPennsylvania Application May 22, 1943, Serial No. 488,003

Claims; (Cl. 219-13) This invention relates to an apparatus for heatingvarious articles by electro-magnetic induc-' tion and has particularreferences to the heating of a number of articles uniformly at the sametime.

In the prior art of inductive heatingit is com-' mon practice to subjectsimultaneously a plurality of articles to the inductive effect of asecondary circuit in a transformer connected to a relatively highfrequency alternating current source. A diillculty appearing inapparatus of this type has been inability toobtain a uniform degree ofheating for each of the various articles and as a consequence some ofthe articles after the completion of the heating process would beunsatisfactory and further treatment would be required or the articlediscarded. It is an important object of the present invention to providea type of inductive apparatus which when applied to a series of'similararticles will produce heating effects in each substantially the same.Other objects contemplated are the provision of means for reducingrejections due to improper heating and the provision of inductionheating means which may be applied without extensive modification inassociated apparatus.

Referring to the drawing wherein is disclosed a form of theinventionwhich may be preferred.

Figure 1 is a view in perspective of the induction heating apparatus asapplied to a series of shells;

Figure 2 is a view of a heating secondary of known typ and Figure 3 is aplan view of a secondary designed to secure uniform heat treatment forall of the heated articles.

In order to illustrate the use of the invention the same is applied toshells for military uses in which it is desirable to silver braze thecap piece, the same being normally screw threaded to the cylindricalbody of the shell. In such two parallel arms 15 and I6 joined by a crossstrip I! at one end, the free ends of the arms terminating in upstandingterminal blocks i8 and I9, the latter serving also as supporting means,by aid of the bolts 20, in attachment to a wall surface. As clearlyshown in the figures the adjoining edges of the arms l5 and ii arerelatively closely spaced as indicated at 2! and at spaced points aseries of semi-circular recesses 22, 23 are formed in these edges sothat the recesses of adjoining edges together form circular areas spacedalong the adjoining surfaces. The size of these circular areas is suchas to receive workpieces such as the various shells hereinbeforementioned, the diameter of the circular areas being greater than that ofthe workpieces so as to permit insertion thereof without establishmentof an electrical contact between the secondary and workpiece.

Supports for the shells are indicated in Figure l, in the formof fiatplates centrally notched and interconnected to form a four wall stand.This stand is placed directly between the circular aperture, the shellbeing centered thereon by a continuation of the stand inside the shellor by other appropriate means.

Referring to the prior art of Figure 2, it is pointed out that the twocircular areas 24 and 25 next to secondary terminals are identical inform whereas the third and outermost circular area 26 diiiers in thatthe end edge 21 is solid instead of slotted. As a result of thisdifference in construction the high frequency secondary current movingin the arms l5 and it of the secondary follows an average path roughlysimilar to that indicated by the dotted line 28. It therefore appearsthat whereas in the case of circular areas 24 and 25 the current followsan approxiassemblies it is desirable that the joint be gas proof andaccordingly after assembly with flux and a ring of silver solder placedat the threaded joint, localized heat is applied inductively to fuse thesolder causing it to seal the joint. Figure 1 illustrates an inductiveapparatus for this form of heat treatment there being shown a base plateIn which at one end has a flange Ii for attachment to a wall surface orother support. Positioned above this plate and spaced therefrom by meansof angle strap i2 is the secondary it, the same being insulated from thestrap by an insulation strip ll. The secondary itisj roughly U shaped inthat it consists of mately identical curved path adjacent the area.edges, in the case of the outermost area26 the current follows a pathcompletely enclosing the outermost section of the area with the resultthat work in this area receives a markedly increased amount of heatthrough this increased coupling of the current flow. This resultobviously prevents uniformity in the heating among the stations.

To overcome the difliculty as above described in the prior art methodand apparatus, applicant extends from the third or outermost circulararea a cleavage 30 in the end plate or strip of the. secondary as shownin Figure 3, the end of this cleavage terminating in a transverse slot3! extending on either side to a point approximately in line with thecommon tangent of the circular areas I, II, and 34. The result of thisconstruction appears when utilized for heating purposes in arearrangement of an average flow of secondary current as indicated bythe dotted line 35 in Figure 3. It is apparent by inspece tion thatthrough the introduction of this transverse slot each of the circularareas including the outermost area is subjected to approximately thesame. pattern of heating current this resulting in the development ofapproximately the same amount of heat in each of the enclosedworkpieces.

While I have shown a transverse slot to secure the desired uniformity ofcurrent flow about the circular aperture it is apparent that other formsof openings may be utilized, the essential requirement being that theopen area 34 by virtue oi the use of the end opening II receive anapproximately equal distribution of heating current. Modifications mayalso be made in the shape of the particular work receiving. aperture oropenings and in the distance between the edges of the aims IS and I andin other details and consequently no limitation is intended by thespecific embodiment of the invention as shown other than is imposed bythe scope of the claims hereunto appended,

What is claimed is:

l. A transformer unit (or inductive heating of work-pieces whichcomprises an electrically conducting plate having a row of workpieceapertures formed therein of uniform lateral diameter, form andalignment, a terminal aperture formed at one end of said row, slotsbetween said apertures and between the workpiece aperture at the end ofsaid row opposite to said terminal aperture and the adjacent plate edge,said plate area lying between and extending outwardly beyond each ofsaid apertures.

2. A transformer unit for inductive heating of workpieceswhich-comprises an electrically conducting plate having a row ofuniformly dimensioned workpiece apertures formed therein with platemetal extending between and outwardly from said apertures, slots betweenthe apertures awards and between the aperture at one end of said row andthe adjacent plate edge and means for esta ing a uniform flow of currentabout each of d apertures.

3 A transformer unit for inductive heating of war pieces-which comprisesan electrically condue ng plate havinga row of uniformly dimensionworkpiece apertures formed along a common axis therein with plate metalextending between and outwardly beyond said apertures, slots betweensaid apertures and between the aperture at one end of said row and theadjacent plate edge and means for establishing a uniform flow of currentabout each of said apertures, said means comprising a plate sectionextending axially from the edge 01' the terminal workpiece apertureopposite to the slotted plate edge having a laterally extending openingtherein, diverse from said workpiece receiving apertures but of the samelateral diameter, and a slot connecting the terminal workpiece apertureand said laterally extending opening.

4. A transverse unit for inductive heating of workpieces each comprisingan electrically conducting plate having. a row of apertures formedtherein along a common axis, uniform slots connecting said aperturesalong the axis thereof, a slot dividing the plate from a terminalaperture and the plate edge to form connector terminals, all saidapertures having the same diameter transverse to said axis and all saidapertures having the same form except the end aperture opposite to theconnector terminals, the plate area lying between and extendinglaterally beyond each of said apertures.

5. Apparatus for heating a plurality of articles by electric currentscomprising a metal plate conductor formed wtih a series of uniform workreceiving apertures, terminal'connectors at one end of said series ofapertures, means for directing current flow between said connectors onopposite sides or the series of apertures, and means for establishinguniformity in current flow about each aperture.

HAROLD A. STRICKLAND, Jr.

